1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device including a light emitting diode (LED) backlight unit where a heat is effectively dissipated.
2. Discussion of the Related Art
A liquid crystal display (LCD) device that has been widely used for a television or a monitor because of its superiority in displaying a moving image and high contrast ratio produces images by using optical anisotropy and polarization properties of liquid crystal molecules. The LCD device includes a liquid crystal panel that is composed of facing two substrates and a liquid crystal layer between the two substrates. An alignment direction of liquid crystal molecules in the liquid crystal panel is changed by an electric field so that the liquid crystal panel can produce difference in transmittance.
Since the LCD device is a non-emissive type display device, an additional light source is required. Accordingly, a backlight unit including a light source is disposed under the liquid crystal panel. Here, one of a cold cathode fluorescent lamp (CCFL), an external electrode fluorescent lamp (EEFL) and a light emitting diode (LED) may be used as the light source. Specifically, the LED has been widely used as a light source for a display device because of its advantages such as small size, low power consumption and high reliability.
FIG. 1 is a cross-sectional view showing a liquid crystal display device including a light emitting diode backlight unit according to the related art. In FIG. 1, a liquid crystal display (LCD) device 1 includes a liquid crystal panel 10, a backlight unit 20, a main frame 30, a top frame 40 and a bottom frame 50.
The liquid crystal panel 10 displaying an image includes first and second substrates 12 and 14 facing and spaced apart from each other and a liquid crystal layer interposed therebetween. The liquid crystal panel 10 further includes first and second polarizing plates 19a and 19b on outer surfaces of the first and second substrates 12 and 14, respectively. The backlight unit 20 is disposed under the liquid crystal panel 10. The backlight unit 20 includes a light emitting diode (LED) assembly 29, a reflecting plate 25, a light guide plate 23 and a plurality of optical sheets 21. The LED assembly 29 is disposed along at least one side of the main frame 30 and the reflecting plate 25 having a white color or a silver color is disposed over the bottom frame 50. In addition, the light guide plate 23 is disposed over the reflecting plate 25 and the plurality of optical sheets 21 are disposed over the light guide plate 23.
The LED assembly 29 disposed on a side of the light guide plate 23 includes a plurality of LEDs 29a emitting a white-colored light and an LED printed circuit board (PCB) 29b where the plurality of LEDs 29a are formed.
The liquid crystal panel 10 and the backlight unit 20 are integrated by the main frame 30, the top frame 40 and the bottom frame 50. The main frame 30 having a rectangular ring shape surrounds an edge portion of the liquid crystal panel 10 and the backlight unit 20. In addition, the top frame 40 covers a front edge portion of the liquid crystal panel 10 and the bottom frame 50 covers a rear surface of the backlight unit 20.
A temperature of the plurality of LEDs 29a increases according to an operating time and a brightness of the plurality of LEDs 29a is changed according to the temperature of the plurality of LEDs 29a. For example, the brightness of the plurality of LEDs 29a decreases as the temperature of the plurality of LEDs 29a increases. Accordingly, a heat dissipation design is required for the backlight unit 20 including the plurality of LEDs 29a to prevent reduction in brightness.
However, since the LCD device 1 according to the related art does not include an effective heat dissipation structure where a heat of high temperature is rapidly released to exterior, the temperature of the plurality of LEDs 29a increases and the brightness of the plurality of LEDs 29a is reduced during operation. As a result, a display quality of the LCD device 1 is deteriorated.